This story has been updated.

Nearly a month after federal courts ordered the U.S. Postal Service to abandon controversial cost-cutting maneuvers that slowed the nation’s mail, on-time delivery rates have dipped again, according to new data released by one of the Senate’s top Democrats.

As millions of voters prepare to vote by mail, the Postal Service gave back five weeks of gains that restored first-class mail delivery service close to levels that predated changes brought on by Postmaster General Louis DeJoy. By the beginning of October, the agency delivered 86 percent of first-class mail on time, down from 90.6 percent before the changes took effect in July, and down from nearly 89 percent at the start of September, according to Postal Service and Postal Regulatory Commission data analyzed by the office of Sen. Gary Peters (Mich.), the chamber’s top Democrat in charge of postal oversight.

The assessment comes as the Postal Service attempts to resolve five overlapping federal court orders that blocked implementation of DeJoy’s cost-cutting agenda. The agency is pushing to restore voters’ and election officials’ confidence in the mail system even as tens of millions of Americans have already received — and millions have cast — their ballots. The Postal Service is preparing to deploy extra personnel and transportation and processing resources in expectation of an influx of ballots. It held a background briefing with journalists earlier in the week to describe its plans for election mail.

Officials said the agency had already delivered a record 417 million pieces of election mail — including ballot applications, voter information and 64 million ballots. That compares with 200 million during the entire 2016 election cycle.

But the agency, represented by Justice Department attorneys, is haggling in federal courts in Pennsylvania, Washington state, New York and the District of Columbia over what directions it should be required to issue to mid-level supervisors and rank-and-file employees about mail processing and delivery during election season.

Judge Victor Marrero in the Southern District of New York ordered the Postal Service to submit a list of steps necessary to restore first-class, on-time delivery rates to 93.9 percent and “make a good-faith effort to fully implement the listed steps,” along with other requirements on deliveries and the authorization of overtime.

Justice Department lawyers sought clarification of that order and argued in a motion this week that maintaining a specific service target would be unmanageable.

“Achieving a target on-time service performance score is a logistical challenge that — despite intensive, good-faith efforts that are underway — may be beyond the Postal Service’s power to overcome in a given week,” acting U.S. Attorney Audrey Strauss wrote.

Lawyers who brought the case on behalf of a group of voters argued to Marrero this week that the troubling decline in service performance meant the Postal Service had not moved aggressively enough to institute those steps.

“Rather than appealing orders they disagree with, the Postal Service seems to be trying to interpret their way out of the various nationwide injunctions having any impact at all,” J. Remy Green, one of the attorneys, said in an interview. “If allowed to continue, that approach — and the resulting shocking drop in service standards — will do grave damage to the right to vote.”

Marrero on Friday held that the Postal Service was making sufficient effort to implement the required steps, and that imposing an independent official to monitor the agency, as the voters urged, could disrupt the Postal Service’s processes close to the election.

Postal Service spokesman David Partenheimer wrote in an emailed statement that delivering election mail was the agency’s top priority and, “We are 100 percent committed throughout the Postal Service to fulfilling our vital role in the nation’s electoral process by securely and timely delivering all ballots pursuant to our long-established processes and procedures.”

The Postal Service’s on-time performance improved the final week of September over the previous week, up 1.7 percent, Partenheimer wrote, because of “our continued focus on the advancement of inventory, reduction in cycle times, and effective use of transportation.”

Also Friday, Sen. Jacky Rosen (Nev.), Peters and 17 other Senate Democrats wrote to DeJoy about problems with the Postal Service’s change-of-address database, which was not updated for three weeks in August.

The agency rectified the problem and restored missing data on Sept. 14, but by then multiple jurisdictions had already sent out election mail, such as mail-in ballot applications, based on the incomplete data. Time magazine first reported the issue last month.

“With voters already casting ballots across the nation, such failures are unacceptable and require immediate action,” the senators wrote.

DeJoy, a former supply-chain logistics executive and major supporter of President Trump, took office on June 15 and within a month enacted a stricter transportation schedule that thrust the agency into chaos. Supervisors were ordered to ban late and extra trips — crucial mechanisms, according to postal workers and independent experts, for maintaining timely mail service — and to cut back on overall hours.

Those orders appear linked to a July 10 presentation from then-Chief Operating Officer David E. Williams to area vice presidents that encouraged a crackdown on late and extra trips and a reduction of work hours. Williams said afterward that the presentation was meant to be “motivational,” not a change in postal policy.

But five weeks after the presentation and as managers gave orders to accomplish those goals, on-time rates plummeted to 81.5 percent, according to Peters’s analysis. In that period, the policies delayed 7 percent of the nation’s first-class mail.

On-time rates rebounded to 88.7 percent the week of Sept. 5, but fell the rest of the month. In the Great Lakes and Capital Metro areas, two of the Postal Service’s seven geographic territories, first-class mail posted its worst numbers of 2020 the week ending Sept. 25.

Service in Detroit, crucial ground that could swing Michigan’s 16 electoral votes in the presidential election, deteriorated further. Eighty-four percent of first-class mail was delivered on-time before DeJoy’s changes, but by the week of Aug. 7, only 61 percent was on-time. Service improved to 83 percent by the beginning of September, but fell back to 72.2 percent by month’s end.